Integrated circuits, active and passive components, optical disk drives, and the like generate heat under use conditions that must be diffused to allow continuous use of the heat-generating component. Heat sinks in the form of finned metal blocks and heat spreaders containing heat pipes are commonly attached to these heat-generating components to allow excess heat to be conducted away and radiated into the atmosphere. Materials useful for providing a thermal bridge between the heat generating components and heat sinks/heat spreaders are known. Many of these materials are based on gel masses, liquid to solid phase change compounds, greases, or pads that must be mechanically clamped between the heat generating component and heat sink/heat spreader.
More recently, thermally conductive materials incorporating adhesives have been introduced. These thermally conductive adhesive materials typically form an adhesive bond between the heat generating component and heat sink/heat spreader so that no mechanical clamping is required. Both heat-activated (hot melt) and pressure sensitive adhesives have been used in thermally conductive adhesives. In all cases, these thermal interface materials need to be thermally enhanced (compared with unfilled or lightly filled polymer compositions), be dimensionally stable at elevated temperatures (heat generating components often run at 50° C. or higher) and be soft and conformable enough to provide good contact (wet-out) between the substrates.
Thermal interface materials can be prepared by a number of known methods. One method is dispersing thermally conductive particles in a low viscosity material, such as a monomer or low molecular weight polymer, followed by polymerization and/or curing and/or crosslinking of the monomer or low molecular weight polymer. For example,f EP Publication No. 0566093 describes preparing thermally conductive electrically insulating pressure sensitive adhesives by blending thermally conductive, electrically insulating particles in reactive monomers and/or oligomers or in a partially photopolymerized syrup, degassing the mixture, coating the composition between two silicone-release treated films, and photopolymerizing the coating to a pressure sensitive adhesive state. Another method is the addition of low molecular weight components to high molecular weight components to provide a suitable viscosity to assist incorporation of the thermally conductive particles. Yet another method is the use of a hot melt coatable PSA composition and crosslinking by use of actinic radiation. Initial attempts with relatively low molar mass hot melt PSA compositions failed to attain good elevated temperature shear performance. Subsequent improvements in this hot melt PSA method have focused on the addition of radiation sensitive, multifunctional, small molecules to improve the crosslinking step. Several different small molecules have been suggested modestly improve elevated temperature shear performance. These methods have certain disadvantages of requiring multiple processing steps and/or multiple component compositions, which add to overall cost of manufacturing.
In some applications, there is a need for rework and/or repair, such as for example, attaching an aluminum frame to a plasma display panel (PDP). In these applications, a thermally conductive adhesive interface article with an easily removable attachment system, such as a stretch-releasable attachment system would be beneficial.
Consequently, it is desirable to provide a simple, cost-effective, method for the manufacture of thermally conductive adhesive interface articles that have acceptable thermal conductivity. It is also desirable to provide the foregoing thermally conductive articles in a fire retardant and/or a stretch-release construction.